Various devices for providing tilt indications for vehicle have been proposed in the prior art. These devices include gravity switching arrangements, such as a body of mercury moving relative to spaced contacts or a swinging conductive pendulum moving in a conducting ring which cooperates with the pendulum to form a switch which is normally open but which closes to energize a warning device when the vehicle reaches a dangerous attitude.
The prior art devices are primarily concerned with non-articulated vehicles, and also do not take into consideration the additional tilt hazards which develop when the vehicle is steered while travelling on a slope. In other words, the prior art devices consider the vehicle to have a substantially fixed stability triangle under all operating conditions. This is not true, especially in the case of articulated vehicles, such as articulated tractors, loaders, forwarders, and other articulated vehicles wherein the center of gravity becomes displaced from its straight-away normal position when the vehicle is frame-steered.
The prior art devices also do not consider the effects on vehicle stability of differences in loading of the vehicle, namely, changes in tilting moments resulting from different loads carried by the vehicle.
Examples of such prior devices are shown in the following prior U.S. patents of interest:
Lawick, U.S. Pat. No. 2,773,953 PA1 Christensen, U.S. Pat. No. 3,359,550 PA1 Pick, U.S. Pat. No. 3,701,093 PA1 Funk, U.S. Pat. No. 3,798,594 PA1 Snead, U.S. Pat. No. 3,921,128 PA1 Dinlocker, U.S. Pat. No. 4,016,535
Also of interest in showing the background of the present invention are the following publications:
Gibson et al, "Side-slope Stability of Articulated-frame Logging Tractors", Jour. of Terramechanics, 8:(92), Pergamon Press, Oxford, England, 65-79, 1971.
Gibson et al, "Stability of Logging Tractors and Forwarders", ASAE Paper No. 71-611, presented at Winter Meeting, Chicago, Ill., Dec. 7-10, 1971, 19 pp.